feat(core): new event streaming by christian-bromann · Pull Request #10772 · langchain-ai/langchainjs

Christian Bromann (christian-bromann) · 2026-04-24T23:25:33Z

Summary

This PR stacks on #10678 and consolidates the new chat model streaming protocol with the agent streaming work from #10697.

The first commit cherry-picks #10697 so the ReactAgent streaming changes can be developed and tested against the new chat model streaming primitives. The remaining commits align the stream event protocol, update the core stream aggregation behavior, refresh the Anthropic adapter, and add/adjust test coverage.

What Changed

Included From #10697

Cherry-picked the agent streaming work from #10697, including support for the new LangGraph streaming primitives in ReactAgent, native toolCalls and middleware stream projections, stream transformer typing, package exports, and related tests.

This PR does not restate all of #10697 in detail; it carries that work here so the chat model stream protocol changes can be validated end-to-end with agent streaming.

Chat Model Stream Protocol Consolidation

Standardized stream events on the event discriminator instead of type.
Renamed message finish response metadata from responseMetadata to metadata.
Simplified content-block-delta events so they carry incremental content: ContentBlock updates directly, instead of a separate delta union.
Widened stream usage inputs to allow partial usage snapshots from providers, while normalizing usage before exposing final AIMessage output.
Made message-finish.reason optional for providers that do not always emit a stop reason.

Core Stream Behavior

Updated ChatModelStream and its typed substreams to consume the consolidated event shape.
Preserved append semantics for text, reasoning, and tool call chunk args.
Kept stable tool call id / name values when later chunks omit them.
Improved reasoning stream handling for reasoning/thinking blocks and finish boundaries.
Changed the usage substream to resolve to undefined when no usage was reported, instead of manufacturing an empty zero-token snapshot.

Compatibility Bridge And Anthropic Adapter

Updated the legacy chunk-to-event bridge to emit the consolidated event format.
Updated Anthropic stream conversion to emit content block updates directly.
Preserved provider passthrough events for Anthropic-specific stream data.
Kept tool call finalization behavior, including JSON argument parsing and invalid tool call handling.

Tests And Environment Coverage

Updated core stream protocol tests, stream assembly tests, and compatibility bridge tests.
Updated Anthropic stream event tests for the consolidated protocol.
Added CJS/export environment coverage needed for the new agent streaming exports.
Added a changeset covering the protocol consolidation.

changeset-bot · 2026-04-24T23:25:37Z

🦋 Changeset detected

Latest commit: a4840ac

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 22 packages

Name	Type
@langchain/core	Patch
@langchain/classic	Patch
langchain	Patch
@langchain/anthropic	Patch
@langchain/cohere	Patch
@langchain/deepseek	Patch
@langchain/fireworks	Patch
@langchain/google-cloud-sql-pg	Patch
@langchain/google-common	Patch
@langchain/google-genai	Patch
@langchain/google-webauth	Patch
@langchain/ibm	Patch
@langchain/neo4j	Patch
@langchain/openai	Patch
@langchain/openrouter	Patch
@langchain/together-ai	Patch
@langchain/xai	Patch
@langchain/model-profiles	Patch
@langchain/standard-tests	Patch
@langchain/google-gauth	Patch
@langchain/google-vertexai-web	Patch
@langchain/google-vertexai	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

Hunter Lovell (hntrl)

For right now I can speak to the public api surface -- I'm fine largely trusting the design decisions behind transformers (though I'm excited to see the readout as someone largely observing from arms length)

Middleware isn't a protocol event right, it's just a projection of node events that we get from inside of a graph?
on chat model events
- I think we need to keep the delta semantics. Right now we extrapolate by just using PartialContentBlock in the delta type, but I think we'd benefit by making these explicit if I'm just thinking about it from a "completions first" perspective
  - Like its not abundantly clear to me that we'd do special handling for named text + reasoning fields (assuming that these come across as token chunks) vs. this third delta type
  - A lot of this is predicated on us having the same idea of how delta merging works which I know was very in flux
- Hopefully we can do away with tool_call_chunk and server_tool_call_chunk if we stick to the three delta types and just have tool call chunks be handled by a merge function that just goes one layer deep when we get that third delta type?

Christian Bromann (christian-bromann) · 2026-04-29T02:07:28Z

Middleware isn't a protocol event right, it's just a projection of node events that we get from inside of a graph?

Correct, both toolCall and middleware stream transformer are just in-process stream projections.

Christian Bromann (christian-bromann) · 2026-04-29T03:22:45Z

I think we need to keep the delta semantics.

Kept delta semantics, see langchain-ai/agent-protocol#78

…ocol

…ol-call-delta, block-delta) - Replace generic DeepPartialContentBlock on delta events with a discriminated union of typed deltas - text-delta/reasoning-delta: append semantics - tool-call-delta: append args, set id/name - block-delta: overwrite semantics for catch-all - Remove accumulated content from delta events (sub-streams now read directly from typed deltas) - Rename chatModelStream() -> streamV2() - Extract bridge logic into compat.ts - Remove createChatModelStream factory (use new ChatModelStream) - Remove type guard functions from event.ts

- Remove ToolCallDelta type; tool call args now use block-delta with accumulated snapshot (adapter accumulates internally) - Rename block-delta.content -> block-delta.fields to avoid confusion with content on start/finish events - Three delta types remain: text-delta (append), reasoning-delta (append), block-delta (overwrite)

Create new-guests-yell.md actually use __native flag more tests and details formatting better fix fix: parse tool call input better middleware typing format add integration tests use eventlog for native stream transformer format keep stream transformer in type bag cr update langgraph update langgraph

github-actions · 2026-05-01T06:07:28Z

📦 Dev Release Published

A dev release has been published for this PR!

Package	Version
@langchain/core	`1.1.43-dev-1777615538778`
@langchain/perplexity	`0.2.0-dev-1777615538778`
langchain	`1.4.0-dev-1777615538778`

Install:

npm i @langchain/core@1.1.43-dev-1777615538778 @langchain/perplexity@0.2.0-dev-1777615538778 langchain@1.4.0-dev-1777615538778 --save-exact

View workflow run

Hunter Lovell (hntrl)

can we split up the langchain-core/langchain changes so we don't have to rely on a dev release?

@jliounis

This PR was opened by the [Changesets release](https://github.com/changesets/action) GitHub action. When you're ready to do a release, you can merge this and the packages will be published to npm automatically. If you're not ready to do a release yet, that's fine, whenever you add more changesets to main, this PR will be updated. # Releases ## @langchain/perplexity@0.2.0 ### Minor Changes - [#10781](#10781) [`1f76917`](1f76917) Thanks [@jliounis](https://github.com/jliounis)! - feat(perplexity): add Perplexity Search retriever (`PerplexitySearchRetriever`) and tool (`PerplexitySearchResults`) ## @langchain/core@1.1.43 ### Patch Changes - [#10814](#10814) [`dfec1b7`](dfec1b7) Thanks [@hntrl](https://github.com/hntrl)! - fix(google): restore structured output parsing with includeRaw and reasoning blocks Ensure structured output parsers read `BaseMessage` text content when `includeRaw: true`, so responses that include reasoning/thought blocks plus JSON text continue to parse correctly. - [#10772](#10772) [`1ba7131`](1ba7131) Thanks [@christian-bromann](https://github.com/christian-bromann)! - chore(core): new stream primitives ## @langchain/google-common@2.1.30 ### Patch Changes - [#10814](#10814) [`dfec1b7`](dfec1b7) Thanks [@hntrl](https://github.com/hntrl)! - fix(google): restore structured output parsing with includeRaw and reasoning blocks Ensure structured output parsers read `BaseMessage` text content when `includeRaw: true`, so responses that include reasoning/thought blocks plus JSON text continue to parse correctly. ## @langchain/google-gauth@2.1.30 ### Patch Changes - Updated dependencies \[[`dfec1b7`](dfec1b7)]: - @langchain/google-common@2.1.30 ## @langchain/google-vertexai@2.1.30 ### Patch Changes - Updated dependencies \[]: - @langchain/google-gauth@2.1.30 ## @langchain/google-vertexai-web@2.1.30 ### Patch Changes - Updated dependencies \[]: - @langchain/google-webauth@2.1.30 ## @langchain/google-webauth@2.1.30 ### Patch Changes - Updated dependencies \[[`dfec1b7`](dfec1b7)]: - @langchain/google-common@2.1.30 ## @langchain/google-genai@2.1.30 Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

## Summary This PR stacks on [langchain-ai#10678](langchain-ai#10678) and consolidates the new chat model streaming protocol with the agent streaming work from [langchain-ai#10697](langchain-ai#10697). The first commit cherry-picks langchain-ai#10697 so the `ReactAgent` streaming changes can be developed and tested against the new chat model streaming primitives. The remaining commits align the stream event protocol, update the core stream aggregation behavior, refresh the Anthropic adapter, and add/adjust test coverage. ## What Changed ### Included From langchain-ai#10697 Cherry-picked the agent streaming work from langchain-ai#10697, including support for the new LangGraph streaming primitives in `ReactAgent`, native `toolCalls` and `middleware` stream projections, stream transformer typing, package exports, and related tests. This PR does not restate all of langchain-ai#10697 in detail; it carries that work here so the chat model stream protocol changes can be validated end-to-end with agent streaming. ### Chat Model Stream Protocol Consolidation - Standardized stream events on the `event` discriminator instead of `type`. - Renamed message finish response metadata from `responseMetadata` to `metadata`. - Simplified `content-block-delta` events so they carry incremental `content: ContentBlock` updates directly, instead of a separate delta union. - Widened stream usage inputs to allow partial usage snapshots from providers, while normalizing usage before exposing final `AIMessage` output. - Made `message-finish.reason` optional for providers that do not always emit a stop reason. ### Core Stream Behavior - Updated `ChatModelStream` and its typed substreams to consume the consolidated event shape. - Preserved append semantics for text, reasoning, and tool call chunk args. - Kept stable tool call `id` / `name` values when later chunks omit them. - Improved reasoning stream handling for reasoning/thinking blocks and finish boundaries. - Changed the usage substream to resolve to `undefined` when no usage was reported, instead of manufacturing an empty zero-token snapshot. ### Compatibility Bridge And Anthropic Adapter - Updated the legacy chunk-to-event bridge to emit the consolidated event format. - Updated Anthropic stream conversion to emit content block updates directly. - Preserved provider passthrough events for Anthropic-specific stream data. - Kept tool call finalization behavior, including JSON argument parsing and invalid tool call handling. ### Tests And Environment Coverage - Updated core stream protocol tests, stream assembly tests, and compatibility bridge tests. - Updated Anthropic stream event tests for the consolidated protocol. - Added CJS/export environment coverage needed for the new agent streaming exports. - Added a changeset covering the protocol consolidation. --------- Co-authored-by: Hunter Lovell <hunter@hntrl.io>

@jliounis

This PR was opened by the [Changesets release](https://github.com/changesets/action) GitHub action. When you're ready to do a release, you can merge this and the packages will be published to npm automatically. If you're not ready to do a release yet, that's fine, whenever you add more changesets to main, this PR will be updated. # Releases ## @langchain/perplexity@0.2.0 ### Minor Changes - [langchain-ai#10781](langchain-ai#10781) [`1f76917`](langchain-ai@1f76917) Thanks [@jliounis](https://github.com/jliounis)! - feat(perplexity): add Perplexity Search retriever (`PerplexitySearchRetriever`) and tool (`PerplexitySearchResults`) ## @langchain/core@1.1.43 ### Patch Changes - [langchain-ai#10814](langchain-ai#10814) [`dfec1b7`](langchain-ai@dfec1b7) Thanks [@hntrl](https://github.com/hntrl)! - fix(google): restore structured output parsing with includeRaw and reasoning blocks Ensure structured output parsers read `BaseMessage` text content when `includeRaw: true`, so responses that include reasoning/thought blocks plus JSON text continue to parse correctly. - [langchain-ai#10772](langchain-ai#10772) [`1ba7131`](langchain-ai@1ba7131) Thanks [@christian-bromann](https://github.com/christian-bromann)! - chore(core): new stream primitives ## @langchain/google-common@2.1.30 ### Patch Changes - [langchain-ai#10814](langchain-ai#10814) [`dfec1b7`](langchain-ai@dfec1b7) Thanks [@hntrl](https://github.com/hntrl)! - fix(google): restore structured output parsing with includeRaw and reasoning blocks Ensure structured output parsers read `BaseMessage` text content when `includeRaw: true`, so responses that include reasoning/thought blocks plus JSON text continue to parse correctly. ## @langchain/google-gauth@2.1.30 ### Patch Changes - Updated dependencies \[[`dfec1b7`](langchain-ai@dfec1b7)]: - @langchain/google-common@2.1.30 ## @langchain/google-vertexai@2.1.30 ### Patch Changes - Updated dependencies \[]: - @langchain/google-gauth@2.1.30 ## @langchain/google-vertexai-web@2.1.30 ### Patch Changes - Updated dependencies \[]: - @langchain/google-webauth@2.1.30 ## @langchain/google-webauth@2.1.30 ### Patch Changes - Updated dependencies \[[`dfec1b7`](langchain-ai@dfec1b7)]: - @langchain/google-common@2.1.30 ## @langchain/google-genai@2.1.30 Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

This PR stacks on [langchain-ai#10678](langchain-ai#10678) and consolidates the new chat model streaming protocol with the agent streaming work from [langchain-ai#10697](langchain-ai#10697). The first commit cherry-picks langchain-ai#10697 so the `ReactAgent` streaming changes can be developed and tested against the new chat model streaming primitives. The remaining commits align the stream event protocol, update the core stream aggregation behavior, refresh the Anthropic adapter, and add/adjust test coverage. Cherry-picked the agent streaming work from langchain-ai#10697, including support for the new LangGraph streaming primitives in `ReactAgent`, native `toolCalls` and `middleware` stream projections, stream transformer typing, package exports, and related tests. This PR does not restate all of langchain-ai#10697 in detail; it carries that work here so the chat model stream protocol changes can be validated end-to-end with agent streaming. - Standardized stream events on the `event` discriminator instead of `type`. - Renamed message finish response metadata from `responseMetadata` to `metadata`. - Simplified `content-block-delta` events so they carry incremental `content: ContentBlock` updates directly, instead of a separate delta union. - Widened stream usage inputs to allow partial usage snapshots from providers, while normalizing usage before exposing final `AIMessage` output. - Made `message-finish.reason` optional for providers that do not always emit a stop reason. - Updated `ChatModelStream` and its typed substreams to consume the consolidated event shape. - Preserved append semantics for text, reasoning, and tool call chunk args. - Kept stable tool call `id` / `name` values when later chunks omit them. - Improved reasoning stream handling for reasoning/thinking blocks and finish boundaries. - Changed the usage substream to resolve to `undefined` when no usage was reported, instead of manufacturing an empty zero-token snapshot. - Updated the legacy chunk-to-event bridge to emit the consolidated event format. - Updated Anthropic stream conversion to emit content block updates directly. - Preserved provider passthrough events for Anthropic-specific stream data. - Kept tool call finalization behavior, including JSON argument parsing and invalid tool call handling. - Updated core stream protocol tests, stream assembly tests, and compatibility bridge tests. - Updated Anthropic stream event tests for the consolidated protocol. - Added CJS/export environment coverage needed for the new agent streaming exports. - Added a changeset covering the protocol consolidation. --------- Co-authored-by: Hunter Lovell <hunter@hntrl.io>

@jliounis

This PR was opened by the [Changesets release](https://github.com/changesets/action) GitHub action. When you're ready to do a release, you can merge this and the packages will be published to npm automatically. If you're not ready to do a release yet, that's fine, whenever you add more changesets to main, this PR will be updated. # Releases ## @langchain/perplexity@0.2.0 ### Minor Changes - [langchain-ai#10781](langchain-ai#10781) [`1f76917`](langchain-ai@1f76917) Thanks [@jliounis](https://github.com/jliounis)! - feat(perplexity): add Perplexity Search retriever (`PerplexitySearchRetriever`) and tool (`PerplexitySearchResults`) ## @langchain/core@1.1.43 ### Patch Changes - [langchain-ai#10814](langchain-ai#10814) [`dfec1b7`](langchain-ai@dfec1b7) Thanks [@hntrl](https://github.com/hntrl)! - fix(google): restore structured output parsing with includeRaw and reasoning blocks Ensure structured output parsers read `BaseMessage` text content when `includeRaw: true`, so responses that include reasoning/thought blocks plus JSON text continue to parse correctly. - [langchain-ai#10772](langchain-ai#10772) [`1ba7131`](langchain-ai@1ba7131) Thanks [@christian-bromann](https://github.com/christian-bromann)! - chore(core): new stream primitives ## @langchain/google-common@2.1.30 ### Patch Changes - [langchain-ai#10814](langchain-ai#10814) [`dfec1b7`](langchain-ai@dfec1b7) Thanks [@hntrl](https://github.com/hntrl)! - fix(google): restore structured output parsing with includeRaw and reasoning blocks Ensure structured output parsers read `BaseMessage` text content when `includeRaw: true`, so responses that include reasoning/thought blocks plus JSON text continue to parse correctly. ## @langchain/google-gauth@2.1.30 ### Patch Changes - Updated dependencies \[[`dfec1b7`](langchain-ai@dfec1b7)]: - @langchain/google-common@2.1.30 ## @langchain/google-vertexai@2.1.30 ### Patch Changes - Updated dependencies \[]: - @langchain/google-gauth@2.1.30 ## @langchain/google-vertexai-web@2.1.30 ### Patch Changes - Updated dependencies \[]: - @langchain/google-webauth@2.1.30 ## @langchain/google-webauth@2.1.30 ### Patch Changes - Updated dependencies \[[`dfec1b7`](langchain-ai@dfec1b7)]: - @langchain/google-common@2.1.30 ## @langchain/google-genai@2.1.30 Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

github-actions Bot added pkg:langchain pkg:@langchain/anthropic labels Apr 24, 2026

Christian Bromann (christian-bromann) force-pushed the cb/new-chat-model-streaming branch from 09f02e8 to d94e7a9 Compare April 27, 2026 20:20

LangChain (langchain-ai) deleted a comment from github-actions Bot Apr 27, 2026

github-actions Bot added the ci label Apr 27, 2026

Christian Bromann (christian-bromann) marked this pull request as ready for review April 27, 2026 20:40

Hunter Lovell (hntrl) reviewed Apr 28, 2026

View reviewed changes

Comment thread libs/langchain-core/src/language_models/event.ts Outdated

Comment thread libs/langchain-core/src/language_models/event.ts Outdated

Comment thread libs/langchain/src/agents/ReactAgent.ts Outdated

LangChain (langchain-ai) deleted a comment from github-actions Bot Apr 29, 2026

LangChain (langchain-ai) deleted a comment from github-actions Bot Apr 30, 2026

LangChain (langchain-ai) deleted a comment from github-actions Bot May 1, 2026

Christian Bromann (christian-bromann) changed the base branch from hunter/chat-model-stream to main May 1, 2026 06:02

Hunter Lovell (hntrl) and others added 9 commits April 30, 2026 23:02

feat(core, anthropic): add content-block-centric streaming event prot…

ece79bd

…ocol

fix: updates to chat model stream / consolidation

8055883

format

ce737a0

update

79b2953

align

6b03d77

type -> event, responseMetadat -> metadata

266086d

Christian Bromann (christian-bromann) force-pushed the cb/new-chat-model-streaming branch from d44cb96 to 9a9b4c2 Compare May 1, 2026 06:04

LangChain (langchain-ai) deleted a comment from github-actions Bot May 1, 2026

Christian Bromann (christian-bromann) changed the title ~~fix: updates to chat model stream / consolidation~~ feat(core): new event streaming May 1, 2026

fix getEventDelta

0776bf5

github-actions Bot added the pkg:@langchain/google-common label May 1, 2026

Christian Bromann (christian-bromann) and others added 2 commits May 1, 2026 14:45

cr

f058750

type cleanup

69f40c6

Hunter Lovell (hntrl) previously approved these changes May 1, 2026

View reviewed changes

github-actions Bot added the ready label May 1, 2026

don't ship middleware transformer

b6485cc

Christian Bromann (christian-bromann) dismissed Hunter Lovell (hntrl)’s stale review via b6485cc May 1, 2026 22:13

Christian Bromann (christian-bromann) added 3 commits May 1, 2026 15:19

tweak

a69e359

revert

1ec7a5d

revert langchain changes

b8cbb05

github-actions Bot removed the pkg:langchain label May 1, 2026

Christian Bromann (christian-bromann) added 2 commits May 1, 2026 15:29

update pnpm-lock

e9af44f

cr

37fc010

github-actions Bot added the pkg:langchain label May 1, 2026

cr

a4840ac

Hunter Lovell (hntrl) approved these changes May 1, 2026

View reviewed changes

Christian Bromann (christian-bromann) merged commit 1ba7131 into main May 1, 2026
39 checks passed

Christian Bromann (christian-bromann) deleted the cb/new-chat-model-streaming branch May 1, 2026 23:45

github-actions Bot mentioned this pull request May 1, 2026

chore: version packages #10787

Merged

Christian Bromann (christian-bromann) mentioned this pull request May 19, 2026

feat(deps): native streamEvents ChatModelStreamEvent protocol #10924

Open

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

feat(core): new event streaming#10772

feat(core): new event streaming#10772
Christian Bromann (christian-bromann) merged 39 commits into
mainfrom
cb/new-chat-model-streaming

Christian Bromann (christian-bromann) commented Apr 24, 2026 •

edited

Loading

Uh oh!

changeset-bot Bot commented Apr 24, 2026 •

edited

Loading

Uh oh!

Hunter Lovell (hntrl) left a comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Christian Bromann (christian-bromann) commented Apr 29, 2026

Uh oh!

Christian Bromann (christian-bromann) commented Apr 29, 2026

Uh oh!

github-actions Bot commented May 1, 2026

Uh oh!

Hunter Lovell (hntrl) left a comment

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

Conversation

Christian Bromann (christian-bromann) commented Apr 24, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Summary

What Changed

Included From #10697

Chat Model Stream Protocol Consolidation

Core Stream Behavior

Compatibility Bridge And Anthropic Adapter

Tests And Environment Coverage

Uh oh!

changeset-bot Bot commented Apr 24, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

🦋 Changeset detected

Uh oh!

Hunter Lovell (hntrl) left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Christian Bromann (christian-bromann) commented Apr 29, 2026

Uh oh!

Christian Bromann (christian-bromann) commented Apr 29, 2026

Uh oh!

github-actions Bot commented May 1, 2026

📦 Dev Release Published

Uh oh!

Hunter Lovell (hntrl) left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

Christian Bromann (christian-bromann) commented Apr 24, 2026 •

edited

Loading

changeset-bot Bot commented Apr 24, 2026 •

edited

Loading