When building provider requests or consuming provider responses, enforce that all intermediate representations match the provider’s expected wire format *at the boundary*—including IDs, message/content blocks, and versioned behavior. Practical rules: 1) **Translate/standardize provider-specific formats at payload-construction time** (don’t assume downstream components share the same schema). - Example: sanitize provider-enforced IDs before sending (Anthropic tool_use.id regex), and normalize multimodal/message content blocks into the standard format expected by the target path. 2) **Validate provider-required structures immediately before API calls**. - Keep validation/normalization in the provider’s formatting/translation layer, not in the base model namespace. 3) **Prevent internal/default flags from leaking into provider payload branching**. - Ensure non-streaming codepaths force `stream=False` *before* payload construction, and strip internal-only kwargs so streaming/non-streaming uses the correct branch. 4) **Make API version behavior explicit per invocation** (e.g., `output_version`) and ensure streaming paths filter internal-only fields. Example (pattern): ```python def _get_request_payload(messages, *, stream: bool, output_version: str | None, tools=None): # 1) validate/translate to wire format messages = normalize_messages_for_provider(messages) # standard blocks/ids if tools is not None: ensure_tool_schemas_present(tools) # avoid provider/token-counter failures # 2) explicit flags: avoid leakage into branching logic kwargs = {"stream": bool(stream)} # 3) explicit versioning: don’t rely on defaults if output_version is not None: kwargs["_output_version"] = output_version payload = build_provider_payload(messages, **kwargs) # 4) strip internal-only keys so they never reach the provider payload.pop("_output_version", None) return payload ``` This standard reduces brittle compatibility bugs where the same higher-level object behaves differently depending on hidden flags, streaming vs non-streaming paths, or provider-specific schema requirements.