On Voyagers return to the Alpha Quadrant they acquired some weapons and technology that would given Starfleet a big tactical advantage (Ablative armour, Transphasic torpedoes and Quantum Slipstream).
Now the armour and the torpedoes may have been confiscated by the temporal police, but not Quantum Slipstream, so my question is:
If Starfleet successfully integrated Quantum Slipstream tech on all of their ships, would they try and keep it a secret or would they share it with the Klingons?
The answer to this question dwells within the lands of SPECULATION.
NOTE: Confiscation of stolen technologies by the Temporal Integrity Commission seems a moot point since the principle for knowing these technologies existed means some crafty engineer with time and a research team should be able to, in a few years, recreate prototypes of the technology, so removing them would only slow their development not stop it.
But for the sake of argument lets assume the transphasic torpedoes and ablative armor from Janeway's 25th Century journey were confiscated. The quantum slipstream drive, however, was acquired legitimately in the Delta Quadrant.
Looking at the very sketchy notes for the Federation-Klingon Alliance I don't see any provisions for technology trade except as the governments decide to. I don't see anything indicating a mandatory sharing of said resources.
The Treaty of Alliance (also known as the Klingon Alliance) was the official agreement that established the alliance between the United Federation of Planets and the Klingon Empire.
Vulcan ambassador Sarek (TNG: "Sarek") was one of the key figures behind the negotiations that created the alliance, and his son, ambassador Spock, was the one who proposed the alliance. (VOY: "Alliances") The Treaty was regarded with controversy when first suggested, but later proved to be a cornerstone for peace in the Alpha Quadrant.
The Federation-Klingon alliance represented a fundamental shift in the balance of power in the Alpha and Beta Quadrants, as the two former enemies united. According to the treaty's terms, each side could request the other's assistance in fighting against its enemies.
This clause, in part, forced the Romulan Star Empire to the sidelines, unable to compete against the combined forces of the Federation and the Klingons. As a result, the Romulans devoted considerable resources towards trying to break up the alliance, albeit without success. (TNG: "Reunion", "The Mind's Eye", "Redemption", "Redemption II")
The Treaty allowed the Federation to conduct health and safety inspections of Klingon vessels within Federation space. It also allowed for unrestricted travel by each side in the other's space. (TNG: "Gambit, Part II")
Several non-canon works address the quantum slipstream drive as a highly coveted technology, that several species were willing to try to steal or go to war over.
