Mellum2.1 Thinking vs Claude Haiku 5.5, head to head

Side A

Side B

Overall

Claude Haiku 5.5 is clearly better. It wins 106 of the 107 test cases where they differ.

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Task by task

A score turns orange only when that model wins clearly more of the task's test cases. Under each score, the average time per test case on the machine it ran on. Mellum2.1 Thinking spends 2.1× as many thinking tokens per test case.

Thinking tokensAnswer tokens

TaskAMellum2.1 ThinkingBClaude Haiku 5.5Mellum2.1 ThinkingClaude Haiku 5.5

Overall

91m 56s

10.3K3.9K

7025.5s

Agents

Runs multi-step jobs through tools, within a written policy

92m 3s

10.8K3.7K

6139.5s

Structured Extraction

Turns logs, diffs and records into exact JSON

51m 36s

8.3K2.6K

9013.5s

Coding

Writes code and SQL that pass hidden tests

52m 11s

11.3K6.8K

8630.6s

Grounded Answers

Answers from the given documents with sources, never guesses

131m 24s

7.3K2.2K

7613.9s

Instruction Following

Applies every rule, including ones changed mid-conversation

283m 10s

17.3K4.3K

9431.5s

Business Logic

Computes billing, scheduling and pricing rules exactly

01m 39s

9K5.5K

6726.0s

Security & permissions

Ignores planted instructions, still does the allowed work

81m 40s

9.1K2.7K

6723.4s

Diagnosis & investigation

Chooses diagnostic checks, repairs supported causes and verifies recovery

01m 15s

6.8K2.3K

1725.5s

What you'd run

The build behind each score. Orange marks the faster, smaller, cheaper or longer-context side.

SpecAMellum2.1 ThinkingBClaude Haiku 5.5

Speed

90 tok/s

225 tok/s

Machine

Apple M5 Pro, 48 GB

Hosted

Memory at 32K

12.9 GB

—

Context

128K

Cost per run

$2.46 est.

$0.42

Cost per case

$0.016 est.

$0.0028

Time per case

1m 56s

25.5s

Quantization

Q8_0

—

Harness

llama.cpp

openrouter

The race

No lead changes

Each model's running score as the test cases go by. The dashed line is a perfect run.

Mellum2.1 ThinkingClaude Haiku 5.5

Every test case

153 test cases

Each square is one test case, colored by the model that scored higher.

Agents012

Structured Extraction018

Coding017

Grounded Answers014

Instruction Following016

Business Logic014

Security & permissions114

Diagnosis & investigation01

1 won by Mellum2.1 Thinking106 won by Claude Haiku 5.546 tied