Dspy Copro

Instruction Optimization with dspy.COPRO

Guide the user through using dspy.COPRO to automatically generate, evaluate, and select the best instructions for their DSPy program's signatures.

Step 1 — Gather context

Before writing code, ask:

1. What does your program do? Which module does it use — Predict, ChainOfThought, a custom dspy.Module? What are the input/output fields?
2. How many labeled training examples do you have? COPRO needs 20-200. Below 20 the search is unreliable; above 200, consider MIPROv2 for joint instruction + demo optimization.
3. Do you have an evaluation metric already, or do you need help writing one? COPRO requires a metric — exact match, semantic similarity, LM-as-judge, etc.
4. Do you want instructions only, or also few-shot demos? If demos would help, use dspy.MIPROv2 instead — it jointly optimizes both and typically outperforms COPRO.

What is COPRO

dspy.COPRO (Collaborative Prompting) is a DSPy optimizer that improves your program by finding better instructions for each signature. Instead of you hand-writing prompt instructions, COPRO generates many candidate instructions, evaluates each one against your metric, and keeps the best.

Key properties:

• Generates instruction candidates -- uses an LM to propose alternative instructions for each predictor in your program
• Evaluates each candidate -- scores every candidate against your metric on the training set
• Iterates in depth -- runs multiple rounds, using top performers from round N to inform candidates in round N+1
• Tunes instructions and prefixes -- optimizes both the signature docstring (instruction) and output field prefixes
• Works with any program -- optimizes all predictors in a program sequentially

When to use COPRO

Use dspy.COPRO when:

• You want to systematically search for better instructions rather than hand-tuning prompts
• You have a metric and 20-200 training examples
• Your program has one or a few predictors that need better instructions
• You want to explore a wide range of instruction phrasings (use high breadth)

Do not use COPRO when:

• You also want to optimize few-shot examples -- use dspy.MIPROv2 instead (it tunes both instructions and demos)
• You have very few examples (<20) and want a lightweight optimizer -- use dspy.GEPA instead
• You want to fine-tune model weights -- use dspy.BootstrapFinetune
• You just need few-shot examples without instruction changes -- use dspy.BootstrapFewShot

Basic usage

Three things are needed: a program, a metric, and training data.

import dspy

dspy.configure(lm=dspy.LM("openai/gpt-4o-mini"))  # or "anthropic/claude-sonnet-4-5-20250929", etc.

# 1. Define a program
classify = dspy.ChainOfThought("text -> label")

# 2. Define a metric
def metric(example, prediction, trace=None):
    return prediction.label.lower() == example.label.lower()

# 3. Prepare training data
trainset = [
    dspy.Example(text="Love this product!", label="positive").with_inputs("text"),
    dspy.Example(text="Terrible experience.", label="negative").with_inputs("text"),
    # ... 20-200 examples
]

# 4. Optimize with COPRO
optimizer = dspy.COPRO(
    metric=metric,
    breadth=10,
    depth=3,
)
optimized = optimizer.compile(
    classify,
    trainset=trainset,
    eval_kwargs=dict(num_threads=4, display_progress=True),
)

# 5. Use the optimized program
result = optimized(text="The quality exceeded my expectations.")
print(result.label)

Constructor parameters

dspy.COPRO(
    prompt_model=None,      # LM for generating candidates (defaults to configured LM)
    metric=None,            # Evaluation function (required)
    breadth=10,             # Number of candidates per iteration (must be >1)
    depth=3,                # Number of optimization iterations
    init_temperature=1.4,   # Temperature for candidate generation
    track_stats=False,      # Collect optimization statistics
)

Compile method

optimized = optimizer.compile(
    student,           # Program to optimize (modified in-place)
    trainset=trainset, # Training examples
    eval_kwargs={},    # Extra kwargs for dspy.Evaluate
)

The returned program has additional metadata:

• optimized.candidate_programs -- dict of all evaluated candidates with their scores
• optimized.total_calls -- total LM API calls made during optimization
• optimized.results_best / optimized.results_latest -- per-iteration best/latest scores (only present when track_stats=True)

The breadth parameter

breadth controls how many instruction candidates COPRO generates per iteration. It is the most important tuning knob.

The first iteration generates breadth - 1 new candidates from the base instruction. Subsequent iterations generate new candidates informed by the best performers so far.

Cost note: Each candidate is evaluated on the full trainset, so total LM calls scale as breadth * depth * len(trainset). With breadth=10, depth=3, and 100 training examples, expect roughly 3,000 evaluation calls plus candidate generation calls.

How COPRO generates candidates

COPRO follows a seeding-and-refinement loop:

1. Seed phase (iteration 0): Takes the existing instruction from each signature. Generates breadth - 1 alternative instructions using temperature-controlled sampling from the prompt model.

2. Evaluate phase: Scores every candidate instruction by swapping it into the program and running the metric against the full training set. Duplicate (instruction, prefix) pairs are skipped.

3. Refine phase (iterations 1 through depth-1): Takes the top-performing candidates from the previous round. Generates new candidates informed by what worked and what did not.

4. Multi-predictor handling: When a program has multiple predictors, COPRO optimizes them sequentially. It locks in the best instruction for predictor 1 before moving to predictor 2, so later predictors benefit from earlier improvements.

5. Selection: After all iterations, the instruction with the highest metric score is selected for each predictor.

Tracking optimization statistics

Enable track_stats=True to see how candidates perform across iterations:

optimizer = dspy.COPRO(
    metric=metric,
    breadth=15,
    depth=3,
    track_stats=True,
)
optimized = optimizer.compile(
    my_program,
    trainset=trainset,
    eval_kwargs=dict(num_threads=4),
)

When track_stats is enabled, COPRO logs per-iteration statistics including max, average, min, and standard deviation of candidate scores. This helps you understand whether the search is converging or whether more breadth/depth would help.

Using a separate prompt model

You can use a stronger (or cheaper) LM specifically for generating instruction candidates:

# Use a strong model to generate candidates, evaluate with the production model
candidate_lm = dspy.LM("openai/gpt-4o")  # or "anthropic/claude-sonnet-4-5-20250929", etc.
production_lm = dspy.LM("openai/gpt-4o-mini")  # or "anthropic/claude-haiku-4-5-20251001", etc.

dspy.configure(lm=production_lm)

optimizer = dspy.COPRO(
    prompt_model=candidate_lm,
    metric=metric,
    breadth=10,
    depth=3,
)
optimized = optimizer.compile(my_program, trainset=trainset, eval_kwargs={})

This is useful when you want a capable model to brainstorm instructions but evaluate and run with a cheaper model.

Comparison with GEPA and MIPROv2

When to pick COPRO over alternatives:

• You want explicit control over the search process (breadth, depth, temperature)
• You want to inspect all candidate instructions and their scores
• You care about instructions specifically, not few-shot examples
• You want a middle ground between GEPA (feedback-driven, competitive with MIPROv2) and MIPROv2 (heavyweight)

When to pick MIPROv2 instead:

• You want the best overall results (MIPROv2 optimizes both instructions and demos)
• You prefer an auto setting over manual tuning of search parameters
• You have enough data (200+) for MIPROv2 to shine

When to pick GEPA instead:

• You have very few examples (<50)
• You want evolutionary search rather than breadth-first generation
• You want something lightweight and fast

Gotchas

• Claude sets breadth=1 which silently breaks optimization. breadth must be greater than 1 — with breadth=1 there are no alternative candidates to evaluate. Use at least breadth=5 for a meaningful search.
• Claude forgets that compile() modifies the student in-place. Unlike most optimizers, COPRO mutates the program you pass to compile(). If you need the original program for baseline comparison, clone it first or create a fresh instance before calling compile().
• Claude passes eval_kwargs as positional instead of keyword. The compile() signature is compile(student, *, trainset, eval_kwargs) — trainset and eval_kwargs are keyword-only. Always use optimizer.compile(program, trainset=trainset, eval_kwargs={}).
• Claude uses COPRO when MIPROv2 would be better. COPRO only optimizes instructions. If the task also benefits from few-shot demonstrations (most tasks do), MIPROv2 optimizes both and typically outperforms COPRO. Use COPRO when you specifically want instruction-only optimization or need to inspect all candidate instructions.
• Claude skips the eval_kwargs parameter. COPRO requires eval_kwargs to be passed to compile(), even if empty. Omitting it causes a TypeError. Always include eval_kwargs={} or eval_kwargs=dict(num_threads=4).

Additional resources

• COPRO API docs
• reference.md — constructor parameters, compile method, candidate inspection
• examples.md — worked examples with breadth search and configuration comparison

Cross-references

Install any skill: npx skills add lebsral/DSPy-Programming-not-prompting-LMs-skills --skill <name>

• Improving accuracy end-to-end (metrics, evaluation, optimizer selection) -- see /ai-improving-accuracy
• MIPROv2 for combined instruction + demo optimization -- see /dspy-miprov2
• GEPA for lightweight instruction tuning -- see /dspy-gepa
• Writing evaluation metrics -- see /dspy-evaluate
• Preparing training data -- see /dspy-data
• Signatures and instructions -- see /dspy-signatures
• Install /ai-do if you do not have it — it routes any AI problem to the right skill and is the fastest way to work: npx skills add lebsral/DSPy-Programming-not-prompting-LMs-skills --skill ai-do