The opinion is here. Based on a quick read, a majority of the court held that:
1. The court declined to overrule Basic Inc. v. Levinson
2. The court left the plaintiff's burden in Basic unchanged. From the syllabus:
The Basic presumption incorporates two constituent presumptions: First, if a plaintiff shows that the defendant’s misrepresentation was public and material and that the stock traded in a generally efficient market, he is entitled to a presumption that the misrepresentation affected the stock price. Second, if the plaintiff also shows that he purchased the stock at the market price during the relevant period, he is entitled to a further presumption that he purchased the stock in reliance on the defendant’s misrepresentation. Requiring plaintiffs to prove price impact directly would take away the first constituent presumption. Halliburton’s argument for doing so is the same as its argument for overruling the Basic presumption altogether, and it meets the same fate. Pp. 16–18.
3. Defendants get a small win with respect to their ability to rebut class certification by showing a lack of price impact. Again, from the syllabus:
The Court agrees with Halliburton, however, that defendants must be afforded an opportunity to rebut the presumption of reliance before class certification with evidence of a lack of price impact. Defendants may already introduce such evidence at the merits stage to rebut the Basic presumption, as well as at the class certification stage to counter a plaintiff’s showing of market efficiency. Forbidding defendants to rely on the same evidence prior to class certification for the particular purpose of rebutting the presumption altogether makes no sense, and can readily lead to results that are inconsistent with Basic’s own logic. Basic allows plaintiffs to establish price impact indirectly, by showing that a stock traded in an efficient market and that a defendant’s misrepresentations were public and material. But an indirect proxy should not preclude consideration of a defendant’s direct, more salient evidence showing that an alleged misrepresentation did not actually affect the stock’s price and, consequently, that the Basic presumption does not apply.