Kimi K3.1 Pro vs Claude Opus 5.5: Half the Price Per Token

Moonshot AI released Kimi K3.1 Pro on October 23 at $2 per 1M input tokens and $10 per 1M output — half of Claude Opus 5.5's list price.

It is the first model of the K3.1 series and a post-trained successor to Kimi K3, the 2.8-trillion-parameter open-weight model Moonshot shipped on July 16, 2026. Two API IDs ship with it: kimi-k3.1-pro and kimi-k3.1-pro-highspeed. Moonshot says full weights for K3.1 Pro arrive by November 4, 2026, and that it stripped cyber-attack material from training before the open release.

What it costs against the flagships

List prices below were compiled by gateway operator Tokely and checked October 24, 2026. Tokely resells access to these models, so treat the roundup as a vendor's table, not a neutral audit.

Model	Input / 1M	Cached input / 1M	Output / 1M
Kimi K3.1 Pro	$2	$0.20	$10
Kimi K3.1 Pro Highspeed	$4	$0.20	$20
Claude Opus 5.5	$4	$0.20	$20
Claude Sonnet 5.5	$2	$0.10	$10
GPT-6.1 Sol (≤272K input)	$2	$0.10	$10
Gemini 4 Argon (to Nov 30)	$2	$0.10	$10

Two prices move on a date. GPT-6.1 Sol shifts to $4 input, $0.20 cached and $15 output above 272K input tokens. Gemini 4 Argon holds its rate until November 30, 2026, then goes to $4 input and $20 output from December 1.

Two workloads decide it

On 1M input plus 250K output, the source puts Kimi K3.1 Pro, Sonnet 5.5, GPT-6.1 Sol and Gemini 4 Argon all at $4.50. Kimi K3 costs $6.75; Opus 5.5 and K3.1 Pro Highspeed both cost $9.00.

On a single 500K-input, 20K-output request, Kimi K3.1 Pro, Sonnet 5.5 and Gemini 4 Argon each land at $1.20, while GPT-6.1 Sol jumps to $2.30 because its long-context tier kicks in above 272K. Opus 5.5 and Highspeed sit at $2.40. Kimi charges one flat rate across its full 1,048,576-token window, with no tiers.

Where Kimi loses

Cached input is the catch. K3.1 Pro bills cache hits at $0.20 per 1M — 10% of its base rate — while Sonnet 5.5 and GPT-6.1 Sol charge $0.10, half as much, at the same $2 base. For agent loops that replay the same system prompt or document set turn after turn, that reverses the ranking. Measure your cache-hit ratio before you switch.

The Highspeed tier is the same model at 2–3× generation speed for exactly double the money, matching Opus 5.5 to the cent. It earns that only where latency is the product: synchronous completion, interactive tooling, customer-facing chat. Batch extraction and offline evals get identical quality at half the price on the standard tier.

What breaks in your code

The API locks temperature to 1.0, top_p to 0.95, n to 1, and both penalties to 0 — Moonshot asks callers to omit them entirely. Thinking is always on and cannot be disabled; reasoning_effort takes low, high or max, defaults to max, and dropping to low is the lever for cutting reasoning time. max_completion_tokens defaults to 131,072 and goes up to 1,048,576. Multi-turn and tool-calling flows must send the complete assistant message back unchanged. Images must be base64 data URLs or uploaded file IDs — public image URLs are rejected. Moonshot says its built-in web search is being updated and is not recommended for production right now.

The K2 clock is running

From October 31, 2026, Kimi K2 models stop being available to newly registered users, and Moonshot plans to retire the whole K2 series by the end of December 2026. Existing users are unaffected by the October date. Teams on Kimi K3 save a third by moving — $3/$15 drops to $2/$10.

On capability, Moonshot's own Terminal-Bench 4.0 numbers put K3.1 Pro at 65.7% against 66.4% for Claude Opus 5.5 and 58.2% for GPT-6 Astra. Those are the vendor's figures and are not independently verified. Direct access needs only a $1 top-up, so the cheap move is to run your own eval set against both tiers before November 4, when the weights land and self-hosting enters the comparison.