Grok 4.6 vs Claude Opus 5.5 API: Pricing, Context, and Reasoning — How to Choose (2026)

TL;DR: On HiAPI, Grok 4.6's unit price is about 40% of Claude Opus 5.5's ($0.84 vs $2.02 input, $2.52 vs $10.08 output, per million tokens). For high-frequency, structured batch tasks that need JSON output, look at Grok 4.6 first. For a 1M context, the native Anthropic Messages protocol, and long-chain Agents and complex coding that need the max thinking tier, choose Claude Opus 5.5. Both only go through /v1/chat/completions (Opus also has /v1/messages), and neither supports /v1/responses — we verified this directly with requests on 2026-11-01.

At a Glance: Specs and Pricing Side by Side

The prices, context, and parameters in the table below come from real-time HiAPI pricing API data on 2026-11-01, and the endpoint and parameter behavior come from real requests we sent that day with a test account.

Dimension	Grok 4.6	Claude Opus 5.5
Model ID	grok-4.6	claude-opus-5-5
Vendor	xAI	Anthropic
Input price (per million tokens)	$0.84 ($1.68 when a single input >200K)	$2.02
Output price (per million tokens)	$2.52 ($5.04 when a single input >200K)	$10.08
Cache hit input (per million tokens)	$0.21 ($0.42 when >200K)	$0.10
Cache write (per million tokens)	No separate billing line	$2.52 (5-minute cache)
Context window	500K	1M
Max single output	500K	128K
Available endpoints	/v1/chat/completions	/v1/chat/completions, /v1/messages
/v1/responses	Not supported (returns 400)	Not supported (returns 400)
Reasoning effort	reasoning_effort: low / medium / high / xhigh	reasoning_effort: low–xhigh; output_config.effort additionally supports max
Tool calling	Supported	Supported
Streaming	Supported, usage in the last chunk	Supported
JSON mode response_format	Supports json_object	Not supported (returns 400)
stop / frequency penalty / presence penalty	Not supported	Not listed in the parameter list

Two things need to be stated upfront:

1. Looking only at unit price distorts the price gap. Grok 4.6 produces reasoning tokens by default, which are billed as output; Opus 5.5 at the low and medium tiers may use very few reasoning tokens on short tasks. Below is a cost comparison from a same-prompt test.
2. Grok 4.6's long context uses tiered pricing. Once a single request's input exceeds 200K tokens, the input, output, and cache prices all double.

Endpoint and Protocol Differences

Both go through Chat Completions, neither goes through Responses

We sent the same prompt to /v1/responses for both models, and both returned:

{"error":{"code":"unsupported_protocol","message":"This model does not support this endpoint. Supported endpoints: /v1/chat/completions. ...","type":"invalid_request_error"}}

Opus 5.5's error message lists /v1/chat/completions, /v1/messages. So if your code is built on the Responses API, you need to switch back to Chat Completions to use these two models.

Opus 5.5 has an extra native Messages channel

On HiAPI, claude-opus-5-5's default protocol is Anthropic Messages (/v1/messages), and it is also compatible with OpenAI Chat Completions. Teams already using the Anthropic SDK or Claude Code can integrate by only changing the base URL and key. Grok 4.6 only offers the OpenAI-compatible protocol.

Reasoning Control: Same Parameter Name, Different Ranges

Both accept reasoning_effort with four tiers: low / medium / high / xhigh. The difference is at the highest tier:

• Passing "reasoning_effort": "max" to Grok 4.6 returns 400 reasoning_effort: is outside allowed values.
• Passing "reasoning_effort": "max" to Opus 5.5 also returns 400, but switching to "output_config": {"effort": "max"} succeeds. This is the only way to turn on max for Opus 5.5.

curl https://api.hiapi.ai/v1/chat/completions \
  -H "Authorization: Bearer $HIAPI_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-opus-5-5",
    "messages": [{"role": "user", "content": "Review this migration script for data loss risks: ..."}],
    "output_config": {"effort": "max"},
    "max_tokens": 8000
  }'

The response structure also differs: Grok 4.6 returns a readable reasoning summary in message.reasoning_content; Opus 5.5 returns thinking blocks with a signature in message.reasoning_details, with the summary text empty. If your frontend needs to display the "thinking process", only Grok 4.6 gives you the text directly.

Tool Calling and Structured Output

We gave both models the same get_order_status function definition, with the user message "help me check where order A1029 is". Both returned finish_reason: "tool_calls", both with the arguments {"order_id":"A1029"}, in the OpenAI tool_calls structure, so one parsing code path works for both.

The structured output difference is clear:

• Grok 4.6 supports "response_format": {"type": "json_object"}. We had it extract a comment into two fields, sentiment and topic, and the returned content was an object ready for json.loads.
• Passing the same parameter to Opus 5.5 returns 400 response_format: is not supported by this execution profile. To get JSON from Opus 5.5, specify the format in the prompt, or use tool-call arguments as structured output.

Also, passing stop to Grok 4.6 returns 400 stop: is unsupported. When migrating from other models, remember to remove stop, frequency_penalty, and presence_penalty from your requests.

Actual Cost on the Same Task

The easiest thing to miscalculate in cost examples is reasoning tokens. We used the same prompt (classifying 3 e-commerce reviews, requiring 3 lines of output), set reasoning_effort: "medium" on both sides, and ran each once in the HiAPI production environment. Results:

	Grok 4.6	Claude Opus 5.5
Classification results	All 3 correct	All 3 correct
Duration	10.1s	6.5s
prompt_tokens	729 (512 of which hit the cache)	480
completion_tokens	651 (622 of which are reasoning)	45
Estimated by unit price	About $0.0019	About $0.0014

(Estimate = uncached input × input price + cached input × cache price + output × output price, using the unit prices in the table above; actual charges are based on the console bill.)

On this short task, Opus 5.5 was actually cheaper, because Grok 4.6 spent 622 reasoning tokens at the medium tier, while Opus 5.5's usage this time had 0 reasoning tokens. This is just a single run and does not represent all tasks; but it shows that for short, quick tasks, choosing Grok 4.6 on unit price alone does not necessarily save money — run your own prompts and check the usage. To cut Grok 4.6's cost, first lower reasoning_effort to low: in the short requests we sent at the low tier that day, reasoning tokens were all under 150.

Switch to long-text tasks where input far exceeds output, and the unit-price gap shows up. Converted from public unit prices:

Scenario	Grok 4.6	Claude Opus 5.5
10K input + 1K output (typical RAG Q&A)	About $0.011	About $0.030
300K input + 4K output (whole-repo code review; Grok enters the >200K tier)	About $0.52	About $0.65
800K input	Exceeds the 500K context, needs splitting	From about $1.62 (fits in the 1M window at once)

The above excludes reasoning tokens; actual output will be more. See the HiAPI pricing page for full unit prices.

How to Choose

Choose Grok 4.6 when you:

• Run large batches of classification, extraction, or rewriting and need json_object mode to get JSON directly;
• Have inputs under 200K and want a lower per-token unit price;
• Need to show the model's reasoning summary to users;
• Need very long single outputs (up to 500K).

Choose Claude Opus 5.5 when you:

• Need to fit 200K–1M tokens of long documents or an entire code repository in one go;
• Already have workflows built on the Anthropic Messages protocol or Claude Code;
• Do long-chain Agents, complex refactoring, and similar tasks that need the max thinking tier;
• Have a lot of repeated system prompts and can benefit from the $0.10 per million cache hit price.

Both are under the same HiAPI key; switching only changes the model field (plus the parameter differences mentioned above), so you can route by task: hand batch preprocessing to Grok 4.6 and final complex reasoning to Opus 5.5.

Checklist for Migration and Switching

1. Use /v1/chat/completions consistently for the endpoint; do not use /v1/responses.
2. Reasoning effort: Grok 4.6 tops out at xhigh; for Opus 5.5's max, pass output_config.effort instead.
3. Remove response_format for Opus 5.5; remove stop and the two penalty parameters for Grok 4.6.
4. Reading reasoning content: for Grok 4.6 look at reasoning_content; for Opus 5.5 look at reasoning_details.
5. For Grok 4.6 streaming, usage is in the last chunk — don't truncate billing stats midway.

For API details, see the HiAPI docs.

FAQ

Which is cheaper, Grok 4.6 or Claude Opus 5.5? By unit price, Grok 4.6's input is about 42% of Opus 5.5's and output about 25%. But Grok 4.6 produces more reasoning tokens, so on short tasks the actual cost may approach or even exceed Opus 5.5. We recommend checking the usage once with your own prompts.

Do both models support the OpenAI-compatible API? Both support /v1/chat/completions. Opus 5.5 also supports Anthropic's native /v1/messages. Neither supports /v1/responses.

Which has a longer context? Claude Opus 5.5 is 1M; Grok 4.6 is 500K. Grok 4.6 charges double unit prices once a single input exceeds 200K.

Which has stronger reasoning? We have not run a systematic benchmark of the two on HiAPI, so we won't draw a conclusion here. Opus 5.5 is positioned for long-running Agent coding and knowledge work and offers five tiers up to max; Grok 4.6 offers four tiers. We recommend running a few comparison rounds with your real tasks.

Can I use both models in one project? Yes. Call both models with the same HiAPI key, just change the model field per task, and billing is unified.

Conclusion

Grok 4.6 wins on unit price, JSON mode, and readable reasoning summaries, making it suitable for batch and structured tasks; Claude Opus 5.5 wins on 1M context, native Messages protocol, max tier thinking, and cheap cache hits, making it suitable for long-context and complex Agents. First try each model's model page with your prompts, check the usage, and then decide. New users get 200 credits upon registration.

Related Reading

• Grok 4.7 vs Grok 4.6: Same Price, Same Context — What's Different and How to Choose
• Claude Opus 5.5 API Pricing: Do the Math by Task
• Opus 5.5 vs GPT-6.1 Sol: A 3-Point Score Gap, an 8x Cost Gap
• Claude Code and Codex on HiAPI: One Key, Choose Models by Task