[Feature] Add reasoning parameter to reasoning models

[Sharath1036]

What feature would you like to see?

dspy.LM takes parameters such as temperature, max_tokens, etc., for LMs as per the LiteLLM format. For reasoning models, they have a parameter called "reasoning" with which we can toggle the reasoning effort. I use reasoning models frequently and require low reasoning effort. So would love this parameter to be added in dspy.LM!

Would you like to contribute?

• Yes, I'd like to help implement this.
• No, I just want to request it.

Additional Context

No response

[joelgrus]

fyi, you can do this with **kwargs, in the chat completions model it's just called reasoning_effort:

https://platform.openai.com/docs/api-reference/chat/create#chat-create-reasoning_effort

In [1]: import dspy

In [2]: default = dspy.LM('openai/gpt-5', temperature=1.0, max_tokens=20000)

In [3]: minimal = dspy.LM('openai/gpt-5', temperature=1.0, max_tokens=20000, reasoning_effort='minimal')

In [4]: %time default('what is the capital of texas')
CPU times: user 137 ms, sys: 42.6 ms, total: 180 ms
Wall time: 2.19 s
Out[4]: ['Austin.']

In [5]: %time minimal('what is the capital of texas')
CPU times: user 11.4 ms, sys: 992 μs, total: 12.4 ms
Wall time: 1.58 s
Out[5]: ['Austin.']

In [6]: %time default('what is the largest prime number')
CPU times: user 11.3 ms, sys: 3.02 ms, total: 14.3 ms
Wall time: 19.4 s
Out[6]: ['There isn’t a largest prime number—there are infinitely many primes.\n\nIf you meant the largest known prime: as of my last update (Oct 2024), the record is a Mersenne prime discovered by GIMPS in December 2023. It’s of the form 2^p − 1 with p about 89.9 million, and has roughly 27 million digits. The record can change, so check the GIMPS site for the latest.']

In [7]: %time minimal('what is the largest prime number')
CPU times: user 12 ms, sys: 73 μs, total: 12.1 ms
Wall time: 3.27 s
Out[7]: ['There is no largest prime number. \n\nEuclid proved over 2,000 years ago that primes go on forever. His classic proof shows that if you assume there’s a largest prime, you can construct a new number that leads to a contradiction—so there must always be more primes.\n\nIf you’re asking about the largest known prime (as of 2025), it’s a Mersenne prime: 2^82,589,933 − 1, discovered in December 2018 by the Great Internet Mersenne Prime Search (GIMPS). It has 24,862,048 digits. New records are found irregularly, so this could change in the future.']