Can I put my accepted paper on arXiv before it appears on the proceedings
The conference did not claim any copyrights!


Are you sure about this? Moreover, even without a copyright transfer or similar, you could have agreed to not having submitted or published the paper elsewhere. If exceptions are being made for publishing preprints, they are often explicit exceptions to clauses that forbid you publishing the article elsewhere, so this is where you should start looking.

If the proceedings are part of a series by some publisher, you may find relevant information on preprint publishability on RoMEO.

If you are still uncertain, you have to ask the conference organisers. I have no experience with such CS conferences, but if journals allow the publication of preprints, this is intentional. Thus I do not see any risk in asking the organisers.