bump retired gemini 2.0 default models to 2.5 (#2433)

gemini-2.0-flash and gemini-2.0-flash-lite are retired and Vertex AI
returns 404 NOT_FOUND for them, hit on a fresh install with the
geminiVertexAI provider and no model set in ModelConfig. Bumps the
defaults to gemini-2.5-flash and gemini-2.5-flash-lite.

---------

Signed-off-by: Petr McAllister <petr.mcallister@gmail.com>
Co-authored-by: Jet Chiang <pokyuen.jetchiang-ext@solo.io>
Co-authored-by: Eitan Yarmush <eitan.yarmush@solo.io>

Author: 3 people

go/adk/examples/oneshot/testdata/gemini.json

@@ -1,7 +1,7 @@
 {
   "model": {
     "type": "gemini",
-    "model": "gemini-2.0-flash"
+    "model": "gemini-2.5-flash"
   },
   "description": "Gemini test agent",
   "instruction": "You are a helpful assistant. Answer concisely in one sentence."

go/adk/examples/oneshot/testdata/gemini_vertexai.json

@@ -1,7 +1,7 @@
 {
   "model": {
     "type": "gemini_vertex_ai",
-    "model": "gemini-2.0-flash"
+    "model": "gemini-2.5-flash"
   },
   "description": "Gemini Vertex AI test agent",
   "instruction": "You are a helpful assistant. Answer concisely in one sentence."

go/adk/pkg/agent/agent.go

@@ -25,7 +25,7 @@ import (
 
 // Default model names used when not specified in configuration
 const (
-	DefaultGeminiModel    = "gemini-2.0-flash"
+	DefaultGeminiModel    = "gemini-2.5-flash"
 	DefaultAnthropicModel = "claude-sonnet-4-20250514"
 	DefaultOllamaModel    = "llama3.2"
 )

go/adk/pkg/agent/agent_test.go

@@ -110,9 +110,9 @@ func TestConfigDeserialization_AllTypes(t *testing.T) {
 		},
 		{
 			name:      "gemini",
-			json:      `{"type":"gemini","model":"gemini-2.0-flash"}`,
+			json:      `{"type":"gemini","model":"gemini-2.5-flash"}`,
 			wantType:  "gemini",
-			wantModel: "gemini-2.0-flash",
+			wantModel: "gemini-2.5-flash",
 		},
 		{
 			name:      "gemini_vertex_ai",

go/core/cli/cmd/kagent/main.go

@@ -261,7 +261,7 @@ If no model is specified, the agent will need to be configured later.
 Examples:
   kagent init adk python dice
   kagent init adk python dice --instruction-file instructions.md
-  kagent init adk python dice --model-provider Gemini --model-name gemini-2.0-flash`,
+  kagent init adk python dice --model-provider Gemini --model-name gemini-2.5-flash`,
 		Args: cobra.ExactArgs(3),
 		Run: func(cmd *cobra.Command, args []string) {
 			initCfg.Framework = args[0]
@@ -279,7 +279,7 @@ Examples:
 	// Add flags for custom instructions and model selection
 	initCmd.Flags().StringVar(&initCfg.InstructionFile, "instruction-file", "", "Path to file containing custom instructions for the root agent")
 	initCmd.Flags().StringVar(&initCfg.ModelProvider, "model-provider", "Gemini", "Model provider (OpenAI, Anthropic, Gemini)")
-	initCmd.Flags().StringVar(&initCfg.ModelName, "model-name", "gemini-2.0-flash", "Model name (e.g., gpt-4, claude-3-5-sonnet, gemini-2.0-flash)")
+	initCmd.Flags().StringVar(&initCfg.ModelName, "model-name", "gemini-2.5-flash", "Model name (e.g., gpt-4, claude-3-5-sonnet, gemini-2.5-flash)")
 	initCmd.Flags().StringVar(&initCfg.Description, "description", "", "Description for the agent")
 
 	buildCfg := &cli.BuildCfg{

helm/kagent/values.yaml

@@ -647,7 +647,7 @@ providers:
       azureEndpoint: ""
   gemini:
     provider: Gemini
-    model: "gemini-2.0-flash-lite"
+    model: "gemini-2.5-flash-lite"
     apiKeySecretRef: kagent-gemini
     apiKeySecretKey: GOOGLE_API_KEY
     # apiKey: ""

python/packages/kagent-adk/tests/unittests/test_instruction_escaping.py

@@ -39,7 +39,7 @@ def _make_agent_config(instruction: str):
     import kagent.adk.types as types_mod
 
     return types_mod.AgentConfig(
-        model={"type": "gemini", "model": "gemini-2.0-flash"},
+        model={"type": "gemini", "model": "gemini-2.5-flash"},
         description="test agent",
         instruction=instruction,
     )

python/samples/adk/basic/basic/agent.py

@@ -42,7 +42,7 @@ async def check_prime(nums: list[int]) -> str:
 
 
 root_agent = Agent(
-    model="gemini-2.0-flash",
+    model="gemini-2.5-flash",
     name="hello_world_agent",
     description=("hello world agent that can roll a dice of 8 sides and check prime numbers."),
     instruction="""