anyllm-proxy/docs/field-mapping.md

Field Mapping: Anthropic -> OpenAI Chat Completions

Request Fields

Anthropic Field	OpenAI Field	Mapping Rule	Notes
model	model	Pass through	Model name kept as-is; aliasing is config-level
max_tokens (required)	max_tokens	Direct copy
system (string)	messages[0] role=developer	Wrap as developer message	Prefer developer over system for newer models
system (blocks)	messages[0] role=developer	Concatenate block texts with newline
messages[].role=user	messages[].role=user	Direct	Content format differs (see below)
messages[].role=assistant	messages[].role=assistant	Direct	Tool calls extracted separately
temperature (0..1)	temperature (0..2)	Pass through	Anthropic range is subset of OpenAI
top_p	top_p	Pass through	Same semantics
stop_sequences[]	stop (string[])	Take first 4	OpenAI caps at 4; silent truncation
stream	stream	Pass through	SSE format translation required
tools[].name	tools[].function.name	Direct
tools[].description	tools[].function.description	Direct
tools[].input_schema	tools[].function.parameters	Direct (JSON Schema)
tool_choice.type=auto	tool_choice="auto"	Simple string
tool_choice.type=any	tool_choice="required"	Semantic equivalent
tool_choice.type=none	tool_choice="none"	Direct
tool_choice.type=tool	tool_choice={type:"function",function:{name}}	Named choice
metadata.user_id	Not mapped	Dropped	No direct equivalent

Content Block Mapping (User Messages)

Anthropic Block	OpenAI Equivalent	Notes
text	text content part	Direct
image (base64)	image_url with data URI	data:{media_type};base64,{data}
image (url)	image_url with URL	Direct
document (base64)	Text note (fallback)	Chat Completions lacks inline PDF support
tool_result	tool role message	Separate message with tool_call_id

Content Block Mapping (Assistant Messages)

Anthropic Block	OpenAI Equivalent	Notes
text	content string	Concatenated if multiple
tool_use	tool_calls[] entry	input (object) -> arguments (JSON string)

Response Fields

OpenAI Field	Anthropic Field	Mapping Rule
choices[0].message.content	content[].type=text	Wrap as text block
choices[0].message.tool_calls	content[].type=tool_use	arguments (string) -> input (object)
choices[0].finish_reason=stop	stop_reason=end_turn
choices[0].finish_reason=length	stop_reason=max_tokens
choices[0].finish_reason=tool_calls	stop_reason=tool_use
choices[0].finish_reason=content_filter	stop_reason=end_turn	Approximate
usage.prompt_tokens	usage.input_tokens	Direct
usage.completion_tokens	usage.output_tokens	Direct
usage.total_tokens	Not mapped	Computed, not stored