Set Anthropic max_tokens to the highest allowed by the model by default (#1979)

Author: DouweM

pydantic_ai_slim/pydantic_ai/models/anthropic.py

@@ -28,6 +28,7 @@
     UserPromptPart,
 )
 from ..profiles import ModelProfileSpec
+from ..profiles.anthropic import AnthropicModelProfile
 from ..providers import Provider, infer_provider
 from ..settings import ModelSettings
 from ..tools import ToolDefinition
@@ -216,11 +217,14 @@ async def _messages_create(
 
         system_prompt, anthropic_messages = await self._map_message(messages)
 
+        max_tokens_limit = AnthropicModelProfile.from_profile(self.profile).anthropic_max_tokens_limit
+        max_tokens = min(model_settings.get('max_tokens', max_tokens_limit), max_tokens_limit)
+
         try:
             extra_headers = model_settings.get('extra_headers', {})
             extra_headers.setdefault('User-Agent', get_user_agent())
             return await self.client.beta.messages.create(
-                max_tokens=model_settings.get('max_tokens', 1024),
+                max_tokens=max_tokens,
                 system=system_prompt or NOT_GIVEN,
                 messages=anthropic_messages,
                 model=self._model_name,

pydantic_ai_slim/pydantic_ai/profiles/anthropic.py

@@ -1,8 +1,40 @@
 from __future__ import annotations as _annotations
 
+from dataclasses import dataclass
+
 from . import ModelProfile
 
 
+@dataclass
+class AnthropicModelProfile(ModelProfile):
+    """Profile for models used with AnthropicModel.
+
+    ALL FIELDS MUST BE `anthropic_` PREFIXED SO YOU CAN MERGE THEM WITH OTHER MODELS.
+    """
+
+    anthropic_max_tokens_limit: int = 1024
+    """The maximum number of tokens that can be generated by this model, as documented at https://docs.anthropic.com/en/docs/about-claude/models/overview. Defaults to 1024."""
+
+
+MAX_TOKENS = {
+    'claude-3-haiku': 4096,
+    'claude-3-opus': 4096,
+    'claude-3-5-haiku': 8192,
+    'claude-3-5-sonnet': 8192,
+    'claude-3-7-sonnet': 64000,
+    'claude-opus-4': 32000,
+    'claude-4-opus': 32000,
+    'claude-sonnet-4': 64000,
+    'claude-4-sonnet': 64000,
+}
+
+
 def anthropic_model_profile(model_name: str) -> ModelProfile | None:
     """Get the model profile for an Anthropic model."""
-    return None
+    max_tokens = 1024
+    for model_prefix, model_max_tokens in MAX_TOKENS.items():
+        if model_name.startswith(model_prefix):
+            max_tokens = model_max_tokens
+            break
+
+    return AnthropicModelProfile(anthropic_max_tokens_limit=max_tokens)