OpenAI API vs Claude API: Check Differences
Compare authentication, request formats, streaming, prompt cache, usage, rate-limit headers and model-purity checks for OpenAI API and Claude API.
Quick Answer
Both APIs need connectivity, TTFT, P95, success-rate and model-identity checks, but their protocol evidence differs. OpenAI checks focus on Responses or Chat Completions, cached_tokens and x-ratelimit headers; Claude checks focus on Messages, cache creation/read tokens and Anthropic rate-limit headers.
Key Takeaways
- The latency framework is shared, but request, usage and cache fields differ.
- OpenAI compatibility does not replace native Anthropic protocol checks.
- Claude exposes cache creation/read tokens; OpenAI commonly exposes cached_tokens.
- Protocol conversion by a relay can remove native evidence.
Core differences at a glance
The same statistical framework can cover both APIs, but probes must understand each native protocol. A gateway that normalizes every provider to OpenAI format can hide Claude cache and rate-limit evidence.
| Area | OpenAI API | Claude API |
|---|---|---|
| Primary API | Responses / Chat Completions | Messages API |
| Authentication | Authorization: Bearer | x-api-key + anthropic-version |
| Streaming | SSE data/events | Typed Anthropic events |
| Cache evidence | cached_tokens | cache creation/read input tokens |
| Rate limits | x-ratelimit-* | anthropic-ratelimit-* |
| Model identity | model | model |
Connectivity and authentication errors
OpenAI failures often involve base URL, bearer keys, model names or endpoint compatibility. Claude also requires the correct anthropic-version, content blocks and max_tokens. Reports should separate authentication, unknown models, schema errors and upstream rate limits.
Streaming and TTFT
Both support TTFT measurement, but meaningful content events differ. OpenAI probes parse delta or Responses events; Claude probes identify content_block_delta and related events. Counting the first data line can mistake metadata for content.
Prompt-cache differences
OpenAI usage commonly exposes prompt_tokens_details.cached_tokens. Claude separates cache creation from cache read tokens and requires correctly marked cacheable content. Claude testing therefore needs paired requests; both providers need a stable long prefix.
Model purity and relay compatibility
Both checks compare model, usage, errors and repeated behavior. A Claude-to-OpenAI relay can lose content blocks, cache and rate-limit fields; OpenAI-compatible gateways often have incomplete tools, streaming or usage.
Choosing the right check template
Use a native Claude template for an Anthropic endpoint. If a supplier offers only an OpenAI-compatible layer, state clearly that the check validates the compatibility layer, not every native Anthropic capability.
Frequently Asked Questions
Can Claude API be checked with an OpenAI template?
Only for a relay that explicitly offers OpenAI compatibility. Some native Anthropic cache, event and rate-limit evidence will be unavailable.
Can TTFT be compared directly between OpenAI and Claude?
Yes, if prompt, output length, region and meaningful-content detection are controlled and each stream protocol is parsed correctly.
Can OpenAI and Claude cache fields be converted directly?
No. Their field semantics and pricing differ. Preserve raw usage and calculate each provider using its own rules.
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